Method of analyzing earth formations



June 1, 1943 H P Q 7 2,320,681 METHOD OF 'ANALYZING EARTH FORMATIONSFiled May 21, 1940 2 Sheets-Sheet l Huberfi Thbmpson,

1; 1 943. H; HGTII-IOMPVSON I 2,320,681"

METHOD-OF ANALYZING EARTH -FOR 1L'*.'1IONS I Fil ed Ma y 21, 1940 '2Sheets-Sine 2 QEOCHEMICAL WELL LOCI MEAN SPECIFIC GRAVITY HYDROCARBUNSATURATION hm" Ian-1s 10,000 by weigh]:

i nzzeiaiarf' Patented June l, 1943 METHOD OF ANALYZING EARTH FORMATIONSHubert R. Thompson, Tulsa, Okla., assignor t, Stanollnd Oil and GasCompany, Tulsa, Okla., a corporation of Delaware Application May 21,1940, Serial No. 336,411

3 plaims.

This invention relates to geochemical well .108- ging, geochemicalprospecting and the analysis of earth formations. It relates moreparticularly to the determination of the hydrocarbon and water contentof drill cuttings from subsurface formations. It also relates, as willhereinafter appear, to the determination of hydrocarbon constituents insoil samples.

It has been found that the presence of various hydrocarbons in drillcuttings from subsurface formationsis related to.the presence of oil andgas deposits within the particular stratum and in somewhat deeperstrata. These constituents which serve as indiciaof the petroleumdeposits include gaseous, liquid and solid materials. The presentinvention relates-principallyto the determination of the liquid,gaseous; and/or solid constituents, notably the former. Moreparticularly this invention is directed to a specific gravity method ofdetermining the hydrocarbon and water content of cuttings or cores fromsubsurface formations. Such determinations can be used in preparing alog of a well, for example in order-to obtain an indication of thepresence and location of oil and gas deposits.-

In making a. geochemical well log, samples-0f the cuttings are taken atfrequent vertically spaced intervals along a well bore. Samples thustaken are analyzed in one way or another for various hydrocarbon orquasi-hydrocarbon constitu- 3 cuts or groups of such constituents andthe re- 'sults for the various samples are compared and plotted in orderto obtain a log of the well which indicates the presence and location ofoil and gas deposits.

It is an object of my invention to provide a new and improved method ofgeochemical well logging and geochemical prospecting. Another object ofthe invention is'to provide a particularly rapid method of analysis ofcore cuttings'and surface soils for hydrocarbon constituents.- A furtherobject is to measure directly the water saturation and the oilsaturation of a core sample from a subsurface formation.

A still further object is to provide a method of this type by which onecan readily determine the proportionate quantities of hydrocarbons inagiven formation having a relatively low density,

or specific gravity and those having a relatively high density orspecific gravity. It is also an obiect of my invention to provide amethod of well logging wherein the total quantity of hydrocarbonspresent in drill cuttings taken during a drilling operation can bedetermined, Other and more detailed objects, advantages and uses of myinvention will become apparent as the description thereof proceeds.

Samples of the drill cuttings or cores taken at selected spaced verticalpoints as previously described are preferably first weighed and crushedtoa grain size approaching that of course sand, and then extracted witha suitable solvent. This extraction can be carried out invarious ways,for instance by leaching or by use of a Soxhlet apparatus. 'It is alsocontemplated that the cuttings as taken from the well can'be heated andimmersed in a cold solvent which will penetrate the pores and extractthe hydrocarbon matter. After the extraction, the solvent extract freedof solid material is placed in a suitable apparatus for determining therelative density of the pure solvent as a reference liquid and theliquid containing dissolved material.

It will be understood, ofcourse, that any solvent or solvent mixturehaving certain solvent properties for hydrocarbon constituents of earthformations such as drill cuttings can be used, so

long as the solvent orsolvent mixture chosen has a specific gravitysubstantially different from that of the hydrocarbon constituentspresent. Just how different the specific gravities must be is determinedby the sensitivity of the apparatus used and by the accuracy desired inthe particular analysis. Examples of organic solvents which can be usedfor the extraction are benzene, cyclo hexane, normal pentane, light.naphtha, carbon disulfide, carbon tetrachloride, and the like. Ifdesired, two extractions of separate portions of the sample may be made,one with a relatively.

low specific gravity solvent and the other with a solvent of relativelyhigh specific gravity. Suitable solvents for the two stage extractionare normal pentane having a specific gravity of about .6300 and carbontetrachloride with a specific ravity of about'l.5835.

Suitable apparatus for the density or specific gravity method ofdetermining hydrocarbons is shown in the drawings, wherein Figures I andII represent partly by diagram, two devices which may be used infollowing my method of analysis. It will be understood, however, thatany method and apparatus which is sufficiently accurate to givecomparative data can be used to determine the density or 'specificgravity of the solvent and solutions. For example, a hydrometer, apycnometer, a Westphal balance, or a Westphal balance type plummet usedon sensitive analytical balances, can be used with considerableaccuracy.

Figure III represents a geochemical well log showing the saturation ofthe formation and the contained therein as a function of the depth atwhich the samples were taken.

Referring to Figure I, the bob I 18 a relative- .ly incompressible floatwhich has been. annealed and carefully ground down so that it 'will justfloat tioned so as to form a continuous tube and permit the flow of thetwo fluids to a new level. Likewise, the reference fluid may be a fluidhaving the same specific gravity as the pure solvent,

in the selected solvent liquid at a standard'temperature, for example 75F. The sensitivity of the bob will depend on its size and can be checkedat'intervals with the pure solvent, but a volume of about c. c. issatisfactory. The glass chamber or reservoir ll encloses the bob l0. Atits lower endis a U-shaped line l2 having a valve l3 and terminating ina funnel or thistle H at .a point above-the fluid level in .the chamberH.

A tube l5 communicates with the reservoir near its top and extends fromthe wall of the chamber ll. Flexible conduit l3 communicates with lineand its free end terminates in thistle IS. The upper end of chamber I l;isprovided with line I6 having valve ll. Athermometer may be providedand from its-reading a correction made from the known coeiflcient ofthermal expansion, instead of attempting accurate temperature control ofthe device, although the latter-means can be used satisfactorily. Scale2| can be calibrated to measure the change in height of the -liquid interms of change in pressure to restore equilibrium. On the other hand,it is also possible and usually preferable to indicate the density orspecific gravity of the dissolved material directly. Because of the lowcoefficient of compression, the reading of applied pressure gives asensitive indication of the amount of compression and hence of thedensity of the extract before compression to restore equilibrium. Theexpansion of the reservoir or leaks through the valves are immaterialsince the compression depends only onthe pressure. Of course, inapplying the pressure, valves l3 and I1 are closed. The glass chamber orreservoir II are filled with the fluid under test and normally the floatbob l0 sinks to the bottom of II. Flexible conduit I8 and thistle l9contain a heavy immiscible fluid such as mercury. With valves l3 and I!closed, pressure on the fluid in II is changed by raising or loweringthe column" of mercury in l8-l9 until the bob It! remains suspended inthe compressed fluid. The heights of mercury and hence the degrees ofcompression of the fluids necessary to increase the specific gravityenough to float the bob ll is an indication of .the comparativedensities of the solvents and extracts. v Another apparatus suitable foruse in my gravimetric method of determining hydrocarbons in an extractliquid is shown in Figure II of the drawings. This device comprises-apair of balanced columns and 3| having common stop,

cock 34 at their lower end and terminating at their free ends withreservoirs 32 and 33'. The entire assembly canbe immersed in a constanttemperature bath; for example a water bath in cylinder 35 at about roomtemperature. A cathetometer 36 can be provided for noting and comparingthe relative heights of the liquid in the balanced columns.

In this device the specific gravity of the solvents containing thehydrocarbons extracted from the bit cuttings is determined by placing inone arm of the balanced columns of the manometer, with the stop cockclosed, a volume of the original pure solvent as a reference fluid andin the other arm, to the same level, the solvent bearing thehydrocarbons. The stop cock is then posiand tube is or some multiple orfraction thereof, and preferably be immiscible therewith.

The proportionate quantities of hydrocarbons having a relatively lowspecific gravity to those having a relatively high specific gravity canbe determined for example, as follows. One portion of the same formationor soil sample may be extracted with a light solvent such as pentane andanother with a heavy solvent such as carbon tetrachloride. The meanspecific gravity of the hydrocarbons extracted by the two solvents can Ivarious samples in order to obtain an indication of the presence andlocation of hydrocarbon deposits. 1

The values of the mean specific gravity and the saturation in terms ofper cent hydrocarbons extracted from the drill .cuttings can be plottedagainst depth to give a complete log of the well.

The specific gravity or relative density rangeswhich indicate theclassification of hydrocarbons the formations are expected to producehave been determined by actual production data obtained in the practiceof my invention.

One specific application of my invention to geochemical well logging isshown in the accompanying Figure 111 which is a log made in the courseof drilling a well in Liberty County, Texas. This log shows thesaturation of the formations and the mean specific gravity of thesoluble materials contained therein, as a function of the depth of thepoints where sampleswere taken.

In preparing this log, samples of bit cuttings were taken from the shaleshaker screen at intervals of one sample each 50 feet of hole drilled-toa depth of 3000 feet. Thereafter samples were taken at intervals of 60feet. The log was plotted sis by air drying in the open air for a periodof about 48 hours.

The quantity of hydrocarbons in these various samples was determined byleaching weighed quantities of them. with standardized amounts of carbontetrachloride and measuring the differencebetween the specific gravityof the original solvent and that of the solution. This difierence wasmeasured using the apparatus of Figure 11,

measuring the difi'erence in the height of the columns in the two armsof the manometer to To determine the mean specific gravity of thehydrocarbons, the change in specific gravity of normal pentane as aleaching agent was determined for those samples showing large amounts oflight substances extracted by carbon tetrachloride. This change inspecific gravity of the normal pentane solvent was determined in themanner above described in the case of carbon tetrachloride. The ratio ofthe difference in column heights when using carbon tetrachloride astween the experimental data and the production data in any given area.

The results of a log of this sort can be improved by,taking samplesduring very short time intervals, in order to make them represent exactdepth. Also rapid methods of drying the samples with a minimum loss ofhydrocarbon content canbe used, in order to minimize the time elapsedbetween the taking of the sample and the availability of the data.

In Figure III the right-hand curve shows the saturation which is theexperimentally determined diflerencebetween the heights of the columnsof the two arms of the manometer of Figure II when using carbontetrachloride as the solvent.

The observed difference in column height is a function of the density ofthe extract solution and also a function of the weight percentage of theThe hydrocarbon saturation is expressed as parts per 10,000 byhydrocarbons dissolved therein.

weight.

As previously indicated, the left-hand curve of Figure III is the meanspecific gravity of the dissolved hydrocarbons determined as abovedescribed. I

The log shown in Figure III indicates a small show of light crude ordistillate at 2800 feet to 2900 feet and somewhat more important showsof gas at 7830 feet continuing to 8220 feet with a slight show ofdistillate at about 8100 feet. Thus,

' the right-hand curve indicates in general the amount of materialpresent, while the left-hand curve indicates its nature.

Earth formations recovered by a core drill can be analyzed veryadvantageously by the methods above described. Cores and drill cuttingshave long been taken from oil-bearing formations or formations which maybe oil-bearing and it is desirable to determine the amount of oilpresent and also something about its probable chemical and physicalnature. Previously available methods for determining'hydrocarbon andwater con-.

tent have been time-consuming and uncertain, while the method abovedescribed can be applied very rapidly'and satisfactorily to all earthformations, including cores, drill cuttings, and soil samples. I

In the, preceding discussion of my invention, it has been described withmore or less particular reference to the use of my method in geochemicalwell logging by the analysis of samples of drill cuttings. It is alsoapplicable, however,.to prosand to the analysis of earth formationsother than drill cuttings. Thus for example, in making a geochemicalsurvey, samples of the surface soil are taken at points along a surveyline or at points spaced over a survey area. The samples thus taken canbe analyzed in accordance with my method and the results compared, inorder to obtain some indication of the presence and location' of deepseated oil and gas deposits which in general correspond to anomalies inthe hydrocarbon composition of the surface soils.

My invention has been described with particular reference to themeasurement of specific gravities but obviously density defined inany'type of unit is satisfactory and, for the purposes of the appendedclaims specific gravity determination is Also merely one form of densitydetermination. since all that is required in geochemical well log- 'gingor geochemical surveying is comparative data, the density units need notalways be known, so long as relative densities for various earthformation samples taken from vertically or horizontally spaced pointsare determined.

While I have described my invention in connection with certain preferredembodiments" thereof, it is to be understood that these are by way ofexample rather than by wayof limitation and I do notmean to berestricted thereto but only to the scope of the appended claims in whichI have defined my invention.

I claim;

1. In a method of prospecting, the steps comprising taking samples ofearth formations, extracting a portion of each of said samples with anorganic solventof relatively high specific gravity, extracting a secondportion of each of said samples with an organic solvent of relativelylow specificgravity, measuring the density of each of the extracts thusformed, and determining the mean specific gravity of the hydrocarbonsextracted from each sample, to secure comparative data indicative of thepresence and location of Y petroleum deposits.

2. In a. method of well logging wherein a plu-' rality of samples ofearth formations are taken at a plurality of vertically spaced points,the improvement comprising treating at least a portion of each of saidsamples with a liquid of known density, recovering at least a portion ofeach of said liquids, separately determining the pressure changenecessary to render the apparent density I of the recovered liquidsequivalent to the initial known density of the treating liquid.

3. In the method-of analyzing earth formations for hydrocarbonconstituents wherein samples are taken from said formations at spacedpoints and treated with a solvent for said hydrocarbons,

the improvement comprising ascertaining the density of an organicsolvent under selected pressure conditions, treating each of a pluralityof earth samples with a portion of the organic sol-, vent, determiningthe density of each of the extracts thus formed, and measuring thechange in pressure necessary to render the apparent density of theextract equivalent to that of the organic solvent alone.

HUBERT H. THOMPSON.

pecting techniques other than that described

